Ebook fundamentals of spun yarn technology part 1

There are three ways of constructing an answer to this question:• To present a classification of yarns • To look at the importance of yarns in fabrics • To analyze various yarn structure

CRC PR E S S

Boca Raton London New York Washington, D.C

Carl A Lawrence, Ph.D.

SPUN YARN TECHNOLOGY

FUNDAMENTALS

of

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Library of Congress Cataloging-in-Publication Data

La wrence, Carl A.

Fundamentals of spun yarn technology / Carl A La wrence.

p cm.

Includes bibliographical references and inde x.

ISBN 1-56676-821-7 (alk paper)

1 Spun yarns 2 Spun yarn industry

3 T e xtile machinery I T itle.

TSI480.L39 2002

CIP

to Mary

Pref ace

The fundamentals of spun-yarn technology are concerned with the production ofyarns from fibers of discrete lengths and the structure-property relation of the spun yarns Ever since humans moved from using the skins of hunted animals for clothing

to farming and using farmed animal hairs and fibers from nonfood crops, and eventually to the manufacture of synthetic fibers, the spinning of yarns has been of importance to (initially) the craft and (subsequently) the science, design, and engi-neering of textiles

This book is aimed at giving the reader a good background on the subject of the conversion of fibers into yarns, and an in-depth understanding of the principles

of the various processes involved It has become popular among some textile nologists to view the subject area as yarn engineering, since there are various yarn structures that, with the blending of different fiber types, enable yarns to be con-structed to meet specific end uses It is therefore necessary for the yarn engineer to have knowledge of the principal routes of material preparation and of the various modern spinning techniques These topics are covered in this book A distinction is made between the terms spinning method and spinning technique by referring to a technique as an implementation of a method, and thereby classifying the many techniques according to methods The purpose is to try to get the reader to identify commonality between spinning systems, something that the author has found useful

tech-in carrytech-ing out research tech-into new sptech-inntech-ing techniques

With any mass-produced product, one essential requirement is consistency of properties For yarns, this starts with the chosen fiber to be spun The yarn technol-ogist has to understand the importance of the various fiber properties used in spec-ifying raw materials, not just with regard to the relation of fiber properties to yarn properties, but especially with respect to the effect of fiber properties on processing performance and yarn quality These aspects are given careful consideration in various chapters throughout the book An understanding of the meaning yarn quality

is seen to be essential; therefore, some effort is devoted to explaining the factors that govern the concept of yarn quality

Textile designers prefer to use the term yarn design rather than yarn engineering,

since the emphasis is often on the aesthetics imparted to the end fabric as opposed

to any technical function Fancy or effect yarns, blends of dyed fibers of different colors, and the plying together of yarns are important topics in yarn design, and the principles and processes employed are described in this book

The material presented is largely that delivered over many years of lecturing and is arranged to be suitable for readers who are new to the subject as well as those who are familiar with the technology and may wish to use this book as a reference source A basic knowledge of physics and mathematics will be helpful to the reader, but is not essential, since a largely descriptive approach has been taken for the

majority of the chapters The few chapters that may be considered more ically inclined present a more detailed consideration to a particular topic and should

mathemat-be easily understood by anyone who has studied physics and mathematics at the intermediate level

Chapter 1 gives a suitable introduction to the subject area by outlining much of the basic concepts and discussing what technically constitutes a spun yarn Chapters

2, 3, 5, 6, 7, and 9 should cover most topics studied by technology students up to graduate level, and Chapter 9 collates material that has been delivered as a module component largely to design students Chapters 4 and 8, and some areas of Chapter

6 that deal with yarn structure-property relation, have been used as topics within a Masters-level module Although, at the advanced level of study, programs are mainly based on current research findings, some areas of the earlier chapters may prove useful for conversion candidates

Throughout the book, definitions are used, where appropriate, in an attempt to give the reader a snapshot of a particular technical point or topic, which is then explained in greater detail It is said that a picture is worth a thousand words, and

in dealing with technical concepts, this is a truism The reader will find, therefore, that effort has been given to fully illustrating the substance of each chapter, and the author hopes that this makes the book a pleasant read for you

A uthor

Carl Lawrence, B.Sc (Applied Physics), Ph.D., is Professor of Textile Engineering

at the University of Leeds and was previously a Senior Lecturer at the University

of Manchester Institute of Science and Technology Before joining academia in 1981,

he worked for 11 years in industrial R&D Many of these years were with the former Shirley Institute, now the British Textile Technology Group (BTTG) In 2002, he was awarded The Textile Institute’s Warner Memorial Medal for his contributions

to investigations in textile technology — in particular, unconventional spinning systems He is the author of many research papers in the field of yarn manufacture and has several patents in the area of open-end spinning

I wish to express my appreciation to the many companies and individuals who gave

me advice, encouragement, and assistance in completing this demanding but able project A special “thank you” to my research colleague and friend Dr Moham-med Mahmoudhi for his time and effort in preparing the majority of the diagrams

Fleissener GmbH & Co

Fratelli Mazoli & Co SpA

Houget Duesberg Bosson

Marzoli

Melliand

Pneumatic Conveyors Ltd

Repco ST

Rieter Machine Works Ltd (Machinenfabrik Rieter)

Rolando Macchine Tessili

Rolando-Beilla

Saurer-Allma GmbH

Savio Macchine Tessili SpA

Spindelfabrik Suessen

The Textile Institute (Journal of the Textile Institute)

TRI (Textile Research Journal)

Trutzschler GmbH & Co KG

W Schlafhorst AG & Co

T able of Contents

Chapter 1 Fundamentals of Yarns and Yarn Production

1.1 Early History and Developments

1.2 Yarn Classification and Structure

1.2.1 Classification of Yarns

1.2.2 The Importance of Yarns in Fabrics

1.2.3 A Simple Analysis of Yarn Structure

1.2.3.1 The Simple Helix Model

1.3 Yarn Count Systems

1.3.1 Dimensions of a Yarn

1.4 Twist and Twist Factor

1.4.1 Direction and Angle of Twist

1.4.2 Twist Insertion, Real Twist, Twist Level, and False Twist1.4.2.1 Insertion of Real Twist

1.4.2.2 Twist Level

1.4.2.3 Insertion of False Twist

1.4.3 Twist Multiplier/Twist Factor

1.4.4 Twist Contraction/Retraction

1.5 Fiber Parallelism

1.6 Principles of Yarn Production

1.7 Raw Materials

1.7.1 The Global Fiber Market

1.7.2 The Important Fiber Characteristics and Properties for Yarn Production

1.7.2.1 Cotton Fibers

1.7.2.1.1 Fiber Length (UHM)1.7.2.1.2 Length Uniformity Index (LUI)1.7.2.1.3 Fiber Strength

1.7.2.1.4 Micronaire1.7.2.1.5 Color1.7.2.1.6 Preparation1.7.2.1.7 Leaf and Extraneous Matter (Trash)1.7.2.1.8 Stickiness

1.7.2.1.9 Nep Content1.7.2.1.10 Short Fiber Content (SFC)1.7.2.2 Wool Fibers

1.7.2.2.1 Fineness1.7.2.2.2 Fiber Length Measurements1.7.2.2.3 Tensile Properties

1.7.2.2.4 Color1.7.2.2.5 Vegetable Content, Grease, and Yield

1.7.2.2.6 Crimp, Bulk, Lustre, Resilience1.7.2.2.7 Medullation

1.7.2.3 Speciality Hair Fibers

1.7.2.3.1 Mohair1.7.2.3.2 Types of Fleeces1.7.2.3.3 Physical Properties1.7.2.3.4 Cashmere

1.7.2.3.5 Physical Properties1.7.2.4 Silk Fibers

1.7.2.4.1 Waste Silk1.7.2.5 Manufactured Fibers [Man-Made Fibers (MMFs)]

1.7.2.5.1 Viscose Rayon and Lyocell1.7.2.5.2 Polyamide (Nylon)1.7.2.5.3 Polyester

1.7.2.5.4 Acrylic1.7.2.5.5 PolypropyleneReferences

Appendix 1A Derivation of Equation for False-Twist Insertion

1A.1 Twist Equation for Zone AX

1A.2 Twist Equation for Zone XB

Appendix 1B Fiber Length Parameters

2.2 Stage I: Opening and Cleaning

2.2.1 Mechanical Opening and Cleaning

2.2.2 Striking from a Spike

2.2.3 Beater and Feed Roller

2.2.4 Use of Air Currents

2.2.5 Estimation of the Effectiveness of Opening and Cleaning Systems

2.2.8.1 Basic Principles of Tuft Blending

2.2.8.2 Tuft Blending Systems

2.2.9 Opening, Cleaning, and Blending Sequence

References

3.2 The Revolving Flat Card

3.2.1 The Chute Feed System

3.2.2 The Taker-in Zone

3.2.3 Cylinder Carding Zone

3.2.4 Cylinder-Doffer Stripping Zone

3.2.5 Sliver Formation

3.2.6 Continuity of Fiber Mass Flow

3.2.7 Drafts Equations

3.2.8 Production Equation

3.2.9 The Tandem Card

3.3 Worsted and Woolen Cards

3.3.1 Hopper Feed

3.3.2 Taker-in and Breast Section

3.3.3 Intermediate Feed Section of the Woolen Card

3.3.3.1 Carding Section

3.3.4 Burr Beater Cleaners and Crush Rollers

3.3.5 Sliver and Slubbing Formation

3.4.1.2 Worsted and Woolen Carding

3.4.2 Nep Formation and Removal

3.4.2.1 Nep Formation

3.4.2.2 The Effect of Fiber Properties

3.4.2.3 Effect of Machine Parameters

3.4.2.4 Short Fiber Content

3.4.3 Sliver and Slubbing Regularity

3.5 Autoleveling

3.6 Backwashing

References

Recommended Readings on the Measurement of Yarn Quality Parameters

Appendix 3A Card Clothing

3A.1 Metallic Wires: Saw-Tooth Wire Clothing

3A.1.1 Tooth Depth

3A.1.2 Tooth Angles

3A.1.3 Point Density

3A.1.4 Tooth Point Dimension

3A.2 Front and Rear Fixed Flats

3A.3 Wear of Card Clothing

Appendix 3B Condenser Tapes and Rub Aprons

Appendix 3C Minimum Irregularity and Index of Irregularity

Chapter 4 Carding Theory

4.1 Opening of Fiber Mass

4.3.1.3 Recycling Layer and Transfer Coefficient

4.3.1.4 Factors that Determine the Transfer Coefficient, K

4.3.1.5 The Importance of the Recycling Layer

4.3.2 Blending-Leveling Action

4.3.2.1 Evening Actions of a Card

4.3.2.1.1 Step Change in Feed4.3.2.1.2 General or Random Irregularities4.3.2.1.3 Periodic Irregularities

4.4 Fiber Breakage

4.4.1 Mechanism of Fiber Breakage

4.4.2 State of Fiber Mass and Fiber Characteristics

4.4.3 Effect Residual Grease and Added Lubrication

4.4.4 Effect of Machine Parameters

4.4.4.1 Tooth Geometry

4.4.4.2 Roller Surface Speed/Setting/Production Rate

4.4.4.2.1 The Taker-in Zone4.4.4.2.2 Effect of Cylinder-Flats and Swift-Worker

InteractionReferences

Appendix 4A

Appendix 4B The Opening of a Fibrous Mass

4B.1 Removal of Fibers when Both Ends are Embedded in the Fiber Mass4B.2 Behavior of a Single Fiber Struck by High-Speed Pins

4B.3 Micro-Damage of Fibers Caused by the Opening Process

and Length5.1.2.3.5 Roller Settings5.1.3 Effect of Machine Defects

5.3 Conversion of Tow to Sliver

6.1.1 Ring and Traveler Spinning Systems

6.1.1.1 Conventional Ring Spinning

6.1.1.2 Spinning Tensions

6.1.1.3 Twist Insertion and Bobbin Winding

6.1.1.3.1 Spinning End Breaks6.1.1.4 Compact Spinning and Solo Spinning

6.1.1.5 Spun-Plied Spinning

6.1.1.6 Key Points

6.1.1.6.1 Advantages6.1.1.6.2 Disadvantages6.1.2 Open-End Spinning Systems

6.1.2.1 OE Rotor Spinning

6.1.2.1.1 Twist Insertion6.1.2.1.2 End Breaks during Spinning6.1.2.2 OE Friction Spinning

6.1.3 Self-Twist Spinning System

6.1.4 Wrap Spinning Systems

6.1.4.1 Surface Fiber Wrapping

6.1.4.1.1 Dref-3 Friction Spinning6.1.4.1.2 Air-Jet Spinning

6.1.4.1.3 Single- and Twin-Jet Systems: Murata

Vortex, Murata Twin Spinner, Suessen Plyfil

6.1.4.2 Filament Wrapping

6.1.5 Twistless Spinning Systems

6.1.5.1 Continuous Felting: Periloc Process

6.1.5.2 Adhesive Bonding: Bobtex Process

6.2 Yarn Structure and Properties

6.2.1 Yarn Structure

6.2.1.1 Surface Characteristics and Geometry

6.2.1.2 Fiber Migration and Helix Model of Yarn Structures6.2.2 Formation of Spun Yarn Structures

6.2.2.1 Conventional Ring-Spun Yarns

6.2.2.1.1 Mechanism of Fiber Migration6.2.2.2 Compact Ring-Spun Yarns

6.2.2.3 Formation of Rotor Yarn Structure

6.2.2.3.1 Cyclic Aggregation6.2.2.3.2 Theory of Spun-in Fibers in Yarns6.2.2.4 Formation of Friction-Spun Yarn Structures

6.2.2.5 Formation of Wrap-Spun Yarn Structures

6.2.2.5.1 Air-Jet Spun Yarns6.2.2.5.2 Hollow-Spindle Wrap-Spun Yarns6.2.3 Structure Property Relation of Yarns

6.2.3.1 Compression

6.2.3.2 Flexural Rigidity

6.2.3.3 Tensile Properties

6.2.3.3.1 Effect of Twist6.2.3.3.2 Effect of Fiber Properties and Material

Preparation6.2.3.3.3 Fiber Blends6.2.3.3.4 Effect of Spinning Machine Variables6.2.3.4 Irregularity Parameters

6.2.3.4.1 Effect of Fiber Properties and Material

Preparation6.2.3.4.2 Effect of Spinning Machine Variables6.2.3.4.3 Yarn Blends

6.2.3.4.4 The Ideal Blend6.2.3.5 Hairiness Profile

7.2.1.2 Grooved Drum

7.2.1.3 Patterning/Ribboning

7.2.1.4 Sloughing-Off

7.2.1.5 Anti-patterning Devices

7.2.1.5.1 Variation of Traverse Frequency, Nt

7.2.1.5.2 Variation of Drum Speed, Nd

7.2.1.5.3 Lifting of Bobbin to Reduce N b

7.2.1.5.4 Rock-and-Roll Method7.2.2 Precision Winding Machines

7.2.3 Advantages and Disadvantages of the Two Methods of Winding

7.2.4 Combinational Methods for Pattern-Free Winding

7.2.4.1 Stepped Precision Winding (Digicone)

7.2.4.2 Ribbon Free Random Winding

7.3 Random-Wound Cones

7.3.1 Package Surface Speed

7.3.2 Abrasion at the Nose of Cones

7.3.3 Traverse Motions

7.4 Precision Open-Wound and Close-Wound Packages

7.4.1 Theory of Close-Wound Packages

7.4.2 Patterning or Ribboning

7.4.3 Hard Edges

7.4.4 Cobwebbing (Webbing or Stitching or Dropped Ends)7.4.5 Twist Displacement

7.5 Yarn Tensioning and Tension Control

7.5.1 Characteristics of Yarn Tensioning Devices

7.5.1.1 The Dynamic Behavior of Yarns

7.5.1.2 The Capstan Effect

7.5.1.3 Multiplicative and Additive Effects

7.5.1.4 Combination Tensioning Devices

8.1.1 Circularly Polarized Standing Waves

8.2 Yarn Tensions in Ring Spinning

8.2.1 Yarn Formation Zone

8.2.2 Winding Zone

8.2.2.1 Yarn Tensions in the Absence of Air Drag

8.2.3 Balloon Zone

8.2.3.1 Balloon Tension in the Absence of Air Drag8.2.3.2 Spinning Tension in the Absence of Air Drag8.2.4 The Effect of Air Drag on Yarn Tensions

8.3 Balloon Profiles in Ring Spinning

8.3.1 Balloon Profiles in the Absence of Air Drag

8.3.2 The Balloon Profile in the Presence of Air Drag

8.3.3 Determination of Ring Spinning Balloon Profiles Based on Sinusoidal Waveforms

8.3.4 Effect of Balloon Control Rings

8.4 Tensions and Balloon Profiles in the Winding Process

8.4.1 Yarn Tensions during Unwinding from a Ring-Spinning Package

8.4.2 Unwinding Balloon Profiles

References

Chapter 9 Fancy Yarn Production

9.1 Classification of Fancy Yarns

9.2 Basic Principles

9.3 Production Methods

9.3.1 Plying Techniques for the Production of Fancy Yarns9.3.1.1 The Profile Twisting Stage

9.3.1.2 The Binding Stage

9.3.1.3 The Plied Chenille Profile

9.3.2 Spinning Techniques for the Production of Fancy Yarns9.4 Design and Construction of the Basic Profiles

F undamentals of Yarns and Yarn Production

Although it has yet to be discovered precisely when man first began spinning fibers into yarns, there is much archaeological evidence to show that the skill was well practiced at least 8000 years ago Certainly, the weaving of spun yarns was developed around 6000 B.C., when Neolithic man began to settle in permanent dwellings and

to farm and domesticate animals Both skills are known to predate pottery, which

We can speculate that early man would have twisted a few fibers from a lock of wool into short lengths of yarn and then tied them together to make longer lengths

We call these staple-spun yarns, because the fibers used are generally referred to as staple fibers Probably the yarn production would have been done by two people working together, one cleaning and spinning the wool, the other winding the yarn into a ball As the various textile skills developed, the impetus for spinning continuous knotless lengths would have led to a stick being used, maybe first for winding up the yarn and then to twist and wind up longer lengths, thereby replacing the making

of short lengths tied together and needing only one operative This method of spinning

a yarn using a dangling spindle or whorl was widely practiced for processing both animal and plant fibers Seeds of domesticated flax (Linum usitassimum) and spindle

1

whorls dating back to circa 6000B.C were found at Ramad, northern Syria, and also

in Samarran villages (Tel-es Swan and Choga Mami) in north Iraq (dated circa 5000

B.C.) In Egypt, at Neolithic Kom, in Fayum, stone and pottery whorls of about 6000

B.C have been discovered, while at the predynastic sites of Omari, near Cairo, and Abydos, both circa 5500 B.C., flax seeds, whorls, bone needles, cloth, and matting have been found

Flax was probably the most common ancient plant fiber made into yarns, though hemp was also used Although flax thread is mentioned in the Biblical records of Genesis and Exodus, its antiquity is even more ancient than the Bible A burial couch found at Gorigion in ancient Phrygia and dated to be late eighth century B.C contained twenty layers of linen and wool cloth, and fragments of hemp and mohair Cotton, native to India, was utilized about 5000 years ago Remnants of cotton fabric and string dating back to 3000 B.C were found at archaeological sites in Indus in Sind (India) Many of these fibers were spun into yarns much finer than today’s modern machinery can produce Egyptian mummy cloth was discovered that had

540 threads per inch in the width of the cloth Fine-spun yarns, plied threads, and plain-weave tabby cloths and dyed garments, some showing darns, were also found

in the Neolithic village of Catal Huyuk in southern Turkey

The simple spindle continued as the only method of making yarns until around

A.D 1300, when the first spinning wheel was invented and was developed in Europe into “the great wheel” or “one-thread wheel.” The actual mechanization of spinning took place over the period 1738 to 1825 to meet the major rise in the demand for spun yarn resulting from the then-spectacular increase in weaving production rates with the invention of the flying shuttle (John Kay, 1733) Pairs of rollers were introduced to thin the fiber mass into a ribbon for twisting (Lewis Paul, 1738); spindles were grouped together to be operated by a single power source—the “water frame” (Richard Arkwright, 1769), the “spinning jenny” (James Hargreaves, 1764–1770) and the “mule” (Samuel Crompton) followed by the “self-acting mule” by Roberts (1825)

In 1830, a new method of inserting twist, known as cap spinning, was invented in the U.S by Danforth In the early 1960s, this was superseded by the ring and traveler,

or ring spinning, which, despite other subsequent later inventions, has remained the main commercial method and is now an almost fully automated process

Today, yarn production is a highly advanced technology that facilitates the engineering of different yarn structures having specific properties for particular applications End uses include not only garments for everyday use and household textiles and carpets but also sports clothing and fabrics for automotive interiors, aerospace, and medical and healthcare applications A detailed understanding of how fiber properties and machine variables are employed to obtain yarn structures of appropriate properties is, therefore, an important objective in the study of spinning technology In this chapter, we shall consider the basics for developing an under-standing of the process details described in the remaining chapters

A good start to our study of staple-yarn manufacture is to consider the question,

“What is a staple-spun yarn?”

There are three ways of constructing an answer to this question:

• To present a classification of yarns

• To look at the importance of yarns in fabrics

• To analyze various yarn structures and identify their most common features

TABLE 1.1

Y arn Classification

Continuous fi lament yarns Untextured (flat) Twisted

Interlaced Tape Textured False twisted

Stuffer box crimped Bi-component Air-jet Staple spun yarns Noneffect/plain

(conventional)

Carded ring spun Combed ring spun Worsted Semi-worsted Woolen Noneffect/plain

(unconventional)

Rotor spun Compact-ring spun Air-jet spun Friction spun Hollow-spindle wrap spun Repco

Fiber blend Blend of two or more fiber types

comprising noneffect yarns Effect/fancy Fancy twisted

Hollow-spindle fancy yarn Spun effects

Composite yarns Filament core

Staple core

Core spun (filament or staple fibers forming the core) and staple fibers as the sheath of a noneffect staple yarn Folded/plied/doubled Filament staple Two or more yarns twisted together

Continuous filament (CF) yarns are basically unbroken lengths of filaments, which include natural silk and filaments extruded from synthetic polymers (e.g., polyester, nylon, polypropylene, acrylics) and from modified natural polymers (e.g., viscose rayon).Such filaments are twisted or entangled to produce a CF yarn.

CF yarns can be subdivided into untextured (i.e., flat) and textured yarns As Table 1.1 shows, CF textured yarns may be further separated into several types; the more commonly used are false-twist textured and air-jet textured yarns For the former, extruded filaments are stretched, then simultaneously heated, twisted, and untwisted, and subsequently cooled to give each filament constituting the yarn a crimped shape and thereby a greater volume or bulk to the yarn (see Figure 1.1) Alternatively, groups of filaments forming the yarn can be fed at different speeds into a compressed-air stream (i.e., an air-jet), producing a profusion of entangled loops at the surface and along the yarn length These processes are known as texturing

or texturizing1,2 and form an area of technology that is outside the context of this book, so they will not be given further consideration The actual principle of false-twisting is used in other processes and is explained in a later section

Continuous filaments can be chopped into discrete lengths, comparable to the lengths of natural plant and animal fibers Both manufactured fibers and natural fibers can be assembled and twisted together to form staple-spun yarns Table 1.1 shows that this category of yarn can be subdivided into plain and fancy yarns In terms of the quantity used, plain yarns are of more technological importance, and the chart indicates the wide range of differing types (i.e., structures) of plain yarn, and thus spinning techniques used to produce them In the later chapters, we shall consider the production of both plain and fancy yarns For the moment, we will confine our attention to plain yarns

1.2.2 T HE I MPORTANCE OF Y ARNS IN F ABRICS

Textile fabrics cover a vast range of consumer and industrial products made from natural and synthetic fibers Figure 1.2 illustrates that, to produce a fabric for a particular end use, the fiber type has first to be chosen and then spun into a yarn

Untextured False Twist Textured Air-jet Textured

(single filament)

FIGURE 1.1 Continuous filament yarns.

structure of specified properties so that the subsequent woven or knitted structure give the desired fabric aesthetics and/or technical performance.

Textile fabrics are also made by means other than knitting and weaving, which may just involve bonding fibers or filaments together without the need of converting them into yarns Although such nonwoven fabrics are an important area of textile manufacturing, especially for technical and industrial end uses, they have limited application in the consumer sector It is reasonable, then, to say that, second only

to fibers from which yarns are made, yarns are the basic building blocks of most textile fabrics Many required fabric properties will, in addition to the fiber properties and the fabric structure, depend on the structure and properties of the constituent yarns Therefore, in the study of yarn manufacture, we need to determine not only how yarns are made but also how to get the required properties for particular end uses To achieve these two goals, we must first establish the factors that characterize

a yarn

1.2.3 A S IMPLE A NALYSIS OF Y ARN S TRUCTURE

In Chapter 6, we will consider in detail the various yarn structures Here, a simple analysis is given so as to answer our question, “What is a staple-spun yarn?”

BASIC SEQUENCE TO GARMENTS

Spinning

CHOICE OF FIBER

(Natural, Manmade, or Blends)

Criteria: Softness, Easy Care, etc.

Figure 1.3 shows highly magnified photographic images of a twisted filament yarn

structure and a typical staple-spun yarn structure (ring-spun yarn)

The following three characteristics are evident:

1 A linear assembly of fibers The assembly could be of any thickness

2 The fibers are held together by twist However, other means may be used

to achieve cohesion

3 There is a tendency for fibers to lie in parallel along the twist spiral

From these three characteristics, we can now answer the question, “What is a

staple-spun yarn?” with the following definition:

A staple-spun yarn is a linear assembly of fi bers, held together, usually

by the insertion of twist, to form a continuous strand, small in cross section

but of any specified length; it is used for interlacing in processes such as

knitting, weaving, and sewing.

The reader should note that there are several other definitions,3,4 but these are more

general, covering filament as well as staple-spun yarns

1.2.3.1 The Simple Helix Model

Based on the three common characteristics, a simplified model can be constructed

to represent yarns in which filaments or fibers are held together by twist, i.e., twisted

yarns Table 1.2 lists the assumptions that are made to construct the model

The manner in which fibers are packed together in the yarn cross section is

important to the effect of frictional contact between fibers on yarn properties If

fibers are loosely packed so that they can move about in the interstitial space, the

yarn will appear bulkier and with a larger diameter than if fibers are closely packed

Two types of packing have therefore been proposed:5close packing, which gives a

hexagonal arrangement of the fibers in the yarn cross section, and open packing,

where the fibers are considered to be arranged in concentric circles of increasing

radii The basic helix model assumes an open packing configuration Figure 1.4

depicts the geometry of the model, and the equations in Table 1.2 give the relations

between the model parameters

FIGURE 1.3 Scanning electron micrograph of continuous filament and ring spun yarn

structure: polyester continuous filament yarn (above) and ring spun yarn (below).

We must consider several important limitations to the basic model.

• Many fibers do not have circular cross sections Furthermore, when fibers

of circular cross sections are inclined at a helix angle of twist, they appear elliptical in the yarn cross section 90° to the yarn axis Thus, only the circular fiber on the yarn axis strictly meets this assumption Nevertheless, fiber diameters are sufficiently small, and generally tend sufficiently toward circular, for the model to remain useful

• In the yarn cross section, the concentric circular layers are filled with

fibers in contact with each other Therefore, if there are N layers ing the yarn, then the arithmetic sum of the number, m, of fibers in each

compris-layer should equal the total amount of fibers in the yarn cross section This, however, is not always so, and the outer layer then becomes partially

filled The result is that the yarn radius, R, is ill defined In practice, there

are many fibers in the cross sections of yarns and correspondingly many circular layers, each only the thickness of one fiber — a few microns in diameter Thus, a partially filled outer layer may not give too great an error

• The model does not take into account the projection of fiber ends from

the yarn surface (termed yarn hairiness) or the relative positions of fiber

ends within the body of a spun yarn The projection of fiber ends from the yarn surface suggests that fiber lengths must move across layers for their ends to become hairs Fibers at the yarn surface must have part of their lengths within the body of the yarn; otherwise, the yarn would not

TABLE 1.2

Assumptions and Geometrical Relations for Helix Yarn Model

Assumptions for helical structure

with open packing of constituent fibers

Geometrical equations defining the helix model

• Yarn composed of a large number of fibers

• The yarn structure consists of a central fiber lying

straight along the yarn axis and surrounded by

successive, concentric cylindrical layers of fibers of

increasing radii.

• The fibers in each layer are helically twisted around

preceding layers.

• The helix angle of twist gradually increases with radius

from 0deg for the central fiber to α for the surface fibers.

• All fibers in a given layer have the same helix angle of

twist

• By convention the yarn twist angle is α

• The turns per unit length is constant throughout yarn

• The fiber packing density is constant throughout the yarn

• A 90-degree cross section to the yarn axis shows the

yarn and fibers to be circular and the fiber cross sections

lying in filled concentric circular layers.

-2πR h

-180 sin1 1

2 n( 1 ) - -

hold together The fibers of a yarn are therefore interlaced The interlacing

of fibers is called migration and is further described in Chapter 6 tion enables the frictional contact between fibers to resist fiber ends slipping past each other When compared with Figure 1.3, the model is clearly more appropriate for continuous filament yarns It can be assumed, however, that, under applied axial loads, where overlapping fiber ends have sufficient frictional contact because of migration and twist, such sections of a staple yarn will approximate the behavior of a continuous filament yarn, and, where insufficient, the ends will slip past each other Hence, by introducing the idea of slippage of overlapping fiber ends, the model can be used to interpret the effect on yarn properties of important geometrical parameters such as twist

Migra-1.3 YARN COUNT SYSTEMS

the dimensions of yarns are expressed In specifying the thickness of a yarn, we could refer to its diameter or radius as in the above model This, however, is not a straightforward parameter to measure Clearly, we would need to assume that the yarn is circular Then, if it were to be measured on a linear scale, we can see from Figure 1.3 that consideration must be given to whether yarn hairiness is included in the measurement.

Straightening the yarn length to measure the diameter involves tensioning the yarn, which also narrows the cross section by bringing fibers into closer contact and increasing the packing density Although there are test methods6 for yarn diameter measurements that attempt to circumvent these difficulties, they are not appropriate for use in the commercial production of yarns Also, in spinning yarns, there is no direct relationship between spinning variables and yarn diameter, so it is not the practice to set up a spinning machine to produce a specified yarn diameter A more useful and practical measure that indirectly gives an indication of yarn thickness is

a parameter that is termed the yarn count or yarn number.

The yarn count is a number giving a measure of the yarn linear density The

linear density is defined as the mass per unit length In Système International (SI)

units, the mass is in grams, and the unit length is meters In textiles, a longer length

is used for greater meaningful measurements, since this would average the small, random, mass variations along the length that are characteristic of spun yarns There are two systems by which the count is expressed, as described below

• Direct system This expresses the count as the mass of a standard length

The mass is measured in grams, and the specific length is either 1 km or

9 km

• Indirect system This gives the length that weighs a standard mass The

standard mass is either 1 kg or 1 lb, and the associated length is, tively, in meters or yards

respec-Usually, thousands of meters of a yarn are required to weigh 1 kg and, similarly, thousands of yards to weigh 1 lb This makes measurements and calculations cum-bersome To circumvent any such awkwardness, a standard length is used The standard length can be 1 km, 840 yd, 560 yd, or 250 yd The standard lengths in

yards are commonly called hanks, or some cases skeins Thus, we can now say that

the indirect system gives the number of kilometers that weigh a kilogram (metric units) or the number of hanks that weigh one pound (English Imperial units) The type of hank being referred to depends on the type of yarn or, more correctly, the manufacturing route used to produce the yarn For carded and combed ring spun yarns, an 840-yd hank is used; a 560-yd hank is associated with worsted and semi-worsted yarns, and a 256-yd hank with woolen yarns Generally, cotton fibers are made by the carded and combed ring spun yarn routes, and synthetic fibers of similar lengths to cotton are made by the carded ring spun route, whereas wool and similar lengths synthetics are processed by the worsted, semi-worsted and woolen routes With respect to the unconventional processes, if a fiber type spun by any of these systems can be also spun by one of the conventional systems, the hank associated with that conventional route is used For example, the production of rotor spun yarns

is usually from cotton and synthetic fibers of cotton lengths, and the 840-yd hank

is therefore used Repco yarns can be made of wool or synthetic fibers of wool lengths, and the 560-yd hank is the applicable standard length

Table 1.3 summarizes the most commonly used units of count for the direct and indirect systems A more comprehensive list can be found in a publication by The Textile Institute, “Textile Terms and Definitions,”4 and a number of the references cited at the end of this chapter give a brief account of the historical origins of several units of the indirect system

Although all the units of count in Table 1.3 are used in practice, we shall use only the tex throughout the remaining chapters of this book The table gives the conversion factors in relation to tex A clear advantage of the tex is that we can refer

to multiples and decimal fractions of the tex in terms of the base 10 scale Thus,

1000 tex = 1 kilotex (ktex), 0.1 tex = decitex (dtex), and 0.001 tex = millitex (mtex)

In this way, the tex unit can be used for fibers and yarns Hence, if we have a yarn

of 100 tex spun from fiber of 1 dtex (0.1 tex), we can estimate the number of fibers

in the yarn cross section to be 1000 A 50-tex yarn should be half the size of a tex, requiring only 500 fibers in its cross section It is the practice to refer to the

100-dtex of a fiber as the fiber fineness; the denier (den) is also used to express fiber

fineness A fiber fineness of 1.5 den is therefore equivalent to 1.7 dtex

Two or more yarns may be twisted together to make a coarser yarn Using the tex unit of count, the resultant yarn count would be the sum of the individual counts

or, if yarns of the same count are twisted together, the product of the number yarns

and the count The process of twisting yarns together is generally known as plying,

folding, or simply twisting, and the resulting yarns as plied or folded yarns The

term doubling is also used when two yarns of the same count are plied, and the

Standard mass unit

Standard length unit

Equivalent tex Direct System

plied yarn is then called a doubled yarn Assume that two 50-tex yarns are doubled;

the resultant yarn count would be 100-tex yarn However, the doubled yarn (i.e., the

two-ply yarn or twofold yarn) may be written as R100/2 tex or just 2/50 tex —

meaning a two-50 tex plied yarn The R denotes resultant count, and the /2 signifies twofold If we let N yarns of the same count, X, be plied, then the plied yarn would

be written as N/X tex and termed an N ply.

Figure 1.5 illustrates the wide count range for the various end uses of filament and staple yarns Besides the very fine yarn count range of 2 to 7.5 tex for hosiery, staple fiber and continuous filament yarns have quite similar market areas, where the fine to medium yarn counts, 7.5 to 40 tex, are largely used to make textiles for

Medium To Fine Yarns

(40–16 tex)

Fine Yarns (16–7.5 tex)

Clothing: Shirts, Blouses, Leisure and Sportswear, etc.

FIGURE 1.5 Count range of product areas for continuous filament and staple spun yarns.

apparel Spun staple yarns hold a principal position in the market for shirts, blouses, home textiles, bed linen, trousers, suits, and so on Filament yarns are highly competitive in the carpet-yarn and sportswear sectors and in the industrial yarn area for technical textiles.

When yarn is sold to a weaver or knitter, one of the buyer’s fundamental concerns

is the length of yarn that gives a specified number of grams per square meter (g/m2) The count system enables the meterage of yarns wound onto bobbins to be sold in terms of the yarn mass of the formed package

After giving some thought to the tex unit, the reader should see that the use of count as an indication of yarn thickness does not take account of the issue of differing fiber densities when comparing the size of yarns spun from different fiber types At times, the bulkiness (i.e., voluminosity) of the yarn is of interest, and then yarn

diameter can either be measured or the equivalent diameter, d y, can be calculated.With reference to the yarn helix model, the yarn diameter is related to the count

as follows:

(1.8)

where δy = the specific volume in g/m3

T t and δy can be measured,7 and d y can be calculated

1.4 TWIST AND TWIST FACTOR

Let us now consider the second of the three identified common characteristics, that

of twist The following four parameters are of importance when discussing twist in yarns:

1 Direction of twist

2 Twist angle

3 Twist level (degree of twist)

4 Twist multiplier

The terms real twist and false twist need also to be explained.

1.4.1 DIRECTION AND ANGLE OF TWIST

From the simple geometrical model of a yarn, the spiral direction and angle of the surface helix, representing the yarn surface fibers, are by convention the direction and twist angle of the yarn In Figure 1.4, the yarn twist angle is α Looking along the axis of the model, the helix has a clockwise direction The spiral direction of a helix may be made counterclockwise The diagonal of the clockwise spiral conforms

to the diagonal of the letter Z, and an counterclockwise spiral to the letter S Thus, the directions of twist are referred to as either Z or S When making microscopic

observations of yarns Matching the inclination of the surface fibers to the center portions of the letters Z and S will determine if the yarn is S-twisted or Z-twisted, and the angle of inclination to the yarn axis would be the twist angle α In Figure 1.3, the CF yarn is S-twisted with a twist angle α = 30°, whereas the ring-spun yarn

is Z twisted and α = 20°

1.4.2 T WIST I NSERTION , R EAL T WIST , T WIST L EVEL , AND F ALSE

T WIST

1.4.2.1 Insertion of Real Twist

The simplest way to insert twist into a strand of fibers (or filaments) is to hold one end (or part) of the strand while the strand length (or the length of the remaining part) is made to rotate on its axis Figure 1.6a illustrates this The strand is nipped

at point A between a pair of stationary rollers while the end, B, is turned to cause rotation of the strand on its own axis The first rotation of the strand will cause the fibers (or filaments) to adopt a helical form, and each subsequent rotation will increase the number of spirals of the helical form and the helix angle, i.e., the number of turns of twist and the twist angle Figure 1.6b shows an alternative situation in which B is now attached to a bobbin placed on a rotating spindle, and

A is still nipped by the rollers, but the length AB is made to bend through the angle

β at M The nipped point A is in line with the spindle axis of rotation As the spindle rotates, the length BM is made to rotate with the spindle, and M circulates the spindle axis Each rotation (circulation) of M will cause the strand to also rotate

on its own axis, thereby inserting twist The twist will initially appear in AM and,

if unrestricted at M, propagate through to B In both situations, the twist inserted

Delivery Rollers

Twisted Filament Strand

Rotating Bobbin Mounted On Spindle

(Angle Of Bend = β)

Vd

Ns

M B

FIGURE 1.6 Real twist insertion.

will remain in the strand and is therefore called real twist If Y is the number of

rotations of M, then the twist per unit length inserted into the strand would be equal

to Y divided by AB Thus, if Y = 100 and AB = 10 cm, the twist inserted would

be 10 turns per centimeter

Consider now the dynamic situation of Figure 1.6b, when the rollers are

deliv-ering the strand to the twisting zone at a delivery speed, V d, of, say, 20 m/min In this situation, if the bend M is made to circulate the spindle axis at a rotational

speed, N s, then the twist inserted would be given by the general formula,

where t = inserted twist (tpm)

N s = rotational speed of the twisting device (rpm)

V d = yarn delivery speed (m/min)

If the speed of M is 10,000 rpm, the twist inserted into the strand would be 500

turns per meter or 5 turns per centimeter If V d were to be increased to 40 m/min

and the twist per unit length kept constant, then the twisting rate would have been doubled, i.e., N s increased to 20,000 rpm

The rotation speed of M should actually be slightly lower than that of the spindle

so that the filament strand can be wound onto the bobbin at the delivery speed V d Some means would be also needed to make the yarn traverse up and down the length

of the bobbin on the spindle during winding This method of twist insertion combined

with winding is used in a commercial process known as ring spinning, which is

described in detail in Chapter 6

1.4.2.3 Insertion of False Twist

Figure 1.7 shows a situation where a strand of filaments, nipped by two pairs of

rollers at A and B, is driven at a linear speed of V d m/min while being twisted at a

rate of N s rpm at some point X along the length spanning the distance between the two sets of rollers If the twisting device is rotating in the direction shown, it will appear to be turning clockwise when viewed along the length AX, and counterclock-wise when viewed along BX Thus, at the start of twisting, Z-twist will be inserted

in the strand as it passes through the AX zone, and S-twist is inserted as it moves through the XB zone As time passes, the Z-twist in the strand length passing through

the AX zone will increase to a constant value of N s /V d In zone XB, S-twist initially will be present in the yarn length passing through the zone; it will increase to a

t = N s /V d

maximum value and then decrease to zero This is because each length of strand moving from zone AX into zone XB will become untwisted by the counterclockwise torque that is present as it enters zone XB A derivation of the equations for Z and

S twist as function of time is given in Appendix 1A

The time over which the Z-twist builds up to its constant value and the S-twist

increases and then decreases to zero may be termed the transient period At the end

of this period, the system is said to be in dynamic equilibrium Z-twist will be observed in the AX zone and no twist will be seen the XB zone This twisting action

is called false-twisting because, under dynamic equilibrium, the strand, although

being twisted, has no twist when it leaves the twisting device A number of spinning systems employ the false-twisting action for producing yarns, and these are also described in Chapter 6

1.4.3 TWIST MULTIPLIER/TWIST FACTOR

The twist angle α has an important influence on yarn properties, as is explained in Chapter 6 It can be seen from the equations defining the yarn helix model that the

twist angle is related to the twist level, t, according to

1000 -

1 2

=

1 2

=

and is called the twist multiple (TM), expressed in turns m–1 tex1/2

With regard to the indirect system of count, Table 1.4 gives the corresponding equations for the Imperial and metric units Note that, with the former, we refer to

the twist factor (TF) and, for the latter, alpha metric (αM)

If there is a change of count but the twist angle, and therefore the twist multiple,

is to remain unchanged, then Equation 1.10 would be used to calculate the required new level of twist For example, with a 25-tex yarn spun at a twist multiplier of 4000

m–1 tex1/2, the twist inserted would be 800 tpm Spinning 16-tex and 64-tex yarns with the same TM would require 1000 tpm and 500 tpm, respectively In practice, different ranges of twist multiples are used in spinning yarns for particular end uses, and Table 1.5 gives examples of the TM range of yarns for knitting and weaving

As indicated in the table, short fibers require a greater level of twist than longer fibers so as to hold together to form a yarn of useful strength The level of twist in

TABLE 1.4

Twist Multiples/Twist Factors

English Imperial (twist factor, TF) TF = , where t is the twist in turns per inch (tpi)

Metric (alpha metric, αM) αM = , where t is the twist in turns per meter (tpm)

TABLE 1.5

TM, TF, and αM Values for Knitting and Weaving

Spinning system End use Twist multiple (TM)

Cottons (staple length < 25mm)

Blends with man-made fibers

Weaving, a warp yarns Weaving, weft yarns

3800–4800 3170–3650 Cottons (staple length > 25 mm)

Blends with man-made fibers

Weaving, warp yarns Hosiery

2400–2860 2050–2550 Wool and blends with man-made fibers Weaving, warp yarns

Weaving, weft yarns Hosiery b

2050–2400 1750–2050 1420–1750

a Warp yarns run the length of woven cloth; weft yarns run across the warp.

b Knitted fabrics and goods made up of them.

a yarn has a strong influence on the yarn properties — in particular, strength, hairiness, and bulk In weaving, warp yarns require more twist than weft yarns, because they need to be of a higher strength and lower hairiness to withstand the tensions and frictional forces of shedding The lower twist gives weft yarns greater bulk, which is imparted to the fabric Knitted fabrics are generally required to have good bulk and softness; consequently, hosiery yarns have the lowest twist levels A

yarn with a high twist level is often referred to as lean and is not suitable for knitwear.

1.4.4 TWIST CONTRACTION/RETRACTION

The insertion of twist gives a small increase in count, referred to as twist contraction.

In Figure 1.4, the simple helix model, if we compared fiber lengths within a yarn length having one turn of twist, we would find that all but the fiber length on the

central axis would be longer than the yarn length That is to say, from the figure, L

> l > h This can be viewed as contraction of the fiber lengths, where h is the contracted length compared with L and l If we imagine cutting a length h from the yarn and then untwisting it to straighten all the fibers, then L and l would be the

untwisted length It should be clear that the count of the untwisted length will be lower than the twisted length; hence, twist contraction As the straightened fiber

lengths will vary, increasing from h at the yarn axis to L at the surface, the untwisted

yarn length is taken as the mean of the straightened fiber lengths.5

Letting L m be the mean untwisted length, we can define the magnitude of length change in two ways

Mean untwisted length – Twisted yarn length

Twisted yarn length

α 1+sec

1.5 FIBER PARALLELISM

The third common structural feature of yarns is the tendency for fibers to lie in a parallel manner When twist is present in the yarn, the fiber parallelism is along the twist direction (see Figure 1.3) We will see, in Chapters 5 and 6, that this orderly arrangement of fibers and therefore the level or degree of fiber parallelism varies between yarn types, some showing some significant randomness Important to the degree of fiber parallelism is fiber shape or configuration within the yarn Where almost all the fibers have their full lengths following the twist helix, as depicted in the Figure 1.3, there is a high degree of parallelism The presence of looped, hooked, and folded fiber configurations and of fibers lying at different twist angles within a fiber layer would significantly reduce the degree of parallelism

The orderly arrangement of fibers in a yarn strongly influences yarn properties and, for the majority of yarns, is dependent on the mechanical actions utilized in processing the fibers up to the point of inserting twist to form the yarn structure It

is therefore appropriate to now describe these basic mechanical actions and their influence on parallelism prior to considering, in the following chapters, the detailed operating principles of the machinery used

1.6 PRINCIPLES OF YARN PRODUCTION

It can be reasoned that to obtain a high degree of fiber parallelism in a yarn, the fibers must be already straight and parallel in the fiber assembly presented for consolidation by twist or some other means Figure 1.8 shows the process sequence for the manufacture of the more common types of staple-spun yarn

When fibers are first purchased for conversion to yarns, they are usually obtained

in large fiber bales At this stage, the fibrous mass is referred to as the raw material;

some raw material may be waste for recycling In the raw material state, fibers have

no definite orientation or configuration A high proportion will be entangled and, in the case of natural fibers like cotton and wool, dirt and vegetable particles and other impurities (e.t., grease) will be present The first stage in a yarn production process

is therefore the cleaning and disentangling of the raw material Where grease has to

be removed, the material is scoured The disentangling of the fiber mass occurs progressively using pin or saw-tooth wire-covered rollers The earlier stages are

collectively referred to as opening and cleaning, since, as the compressed fiber mass

is opened up, solid impurities are released to become waste The final stage of

disentanglement is called carding, where the fiber mass is separated into individual fibers that are collected together to form a twistless rope termed a card sliver Because

of the carding process, the fiber orientation is very close to the sliver axis; therefore, carding may be considered as the start of the parallel arrangement of fibers However, only very few fibers in a card sliver have a straightened shape

To straighten hooked and folded fibers, and greatly improve fiber alignment along the sliver axis, the sliver is thinned by stretching; the mechanical action is

called drafting, and the amount by which it is stretched is the draft Clearly, the

count of the sliver will decrease, so drafting is an attenuating action, and the draft

is equal to the factor by which the sliver count is reduced Thus, if a 6-ktex sliver

is reduced by a draft of 3, a 1-m length would be stretched to 3 m, and the resulting sliver count would be 2 ktex This means that

(1.11)

The drafting of the sliver gives rise to shear within the fiber mass; fibers slide past each other as the sliver is stretched, giving the permanent extension or elonga-tion The friction contact between fibers during the sliding motion straightens and aligns fibers along the sliver axis Figure 1.9 shows the situation where two pairs

Back Washing

Shrink Proofing

Top Dyeing

Combing

Roving

Production

Roving Production

Spinning

Winding

Rewinding Plying

Combed Ring-Spun Yarn

Carded Ring Spun Yarn

Rotor Spun Yarn

I Opening and Cleaning II Fiber Disentangling and Cleaning III Fiber Straightening and Parallelization (Short Fiber Removal + Additional Cleaning)

IV Fiber Straightening, Parallelization, Attenuation V Yarn Formation

Carding

Gilling

Gilling

Preparation Sorting, Scouring, Carbonizing, Stock- Dyeing, Blending

Stretch Break Carding

Rebreak Combing

Gilling

FIGURE 1.8 Yarn production process sequence.

Draft stretched length

initial length

- initial count (tex)

final count (tex) -

of rollers are used for drafting The bottom rollers are fluted metal rollers that are driven through a set of gears by an electric motor The flutes may be straight, as illustrated in Figure 1.9, or given a slight spiral The top rollers are synthetic-rubber-

covered rollers and are pressured down onto the bottom rollers (termed weighted

down) and driven through frictional contact The compression, referred to as the hardness, of the synthetic rubber cover can be varied to suit the fiber frictional

properties The flutes of the bottom rollers and the resilience of the top rollers are important for the nipping of fibers during drafting

The diagram illustrates what is called a single drafting zone arrangement, and the method of drafting is termed roller drafting There are other methods of drafting,

and these are described in the later chapters wherein we consider the processes in which they are used The basic idea of drafting is explained here, using roller drafting

as an example

The drafting zone in which the material is stretched and attenuated is the horizontal area between the nip lines of the two pairs of rollers The material is fed

into the zone at the surface speed, V1, of rollers A and pulled out of the zone by

rollers B at speed V2 Thus, Equation 1.11 can be rewritten,

(1.12)

Ideally, where two fibers, x and y, are in frictional contact with the leading end

of x nipped by rollers B while its trailing end is free, and the converse is true for y with roller A, then the sliding of x past y will be effective in straightening and aligning the fibers along the sliver axis Even if we were to assume that fibers forming the card sliver were of equal lengths, there will be differing fiber shapes (i.e., configurations) giving different extents and orientations to the sliver axis Conse-

x y

A

B

+ V1

- initial count (tex)

final count (tex) -

quently, on the first pass of the sliver through the drafting zone, there would be fibers that are not nipped effectively to be straightened and aligned The use of more than one drafting zone and the passing of the material through the drafting process several times therefore would be beneficial In practice, the process stage after

carding, known as drawing, involves six or eight card slivers of the same count being

drafted to the count of one sliver, and the drawing passage repeated with six or eight

of the first drawn sliver Up to three drawing passages can be used Chapter 5describes in more detail the drawing processes used in the production of staple yarns

In bringing six or eight slivers together, termed a doubling of six or eight, and applying to them a draft of six or eight, the resulting sliver will comprise a sixth or

an eighth of the count (and also of the number of fibers in the cross section) of each original sliver Repeating the process further reduces the proportion to 1/36 or 1/64 There is, in effect, a blending of the original slivers, and the greater the number of drawing passages, the better the blending This blending by doubling of slivers improves the uniformity of the final slivers and, ultimately, that of the spun yarn Drawing is, therefore, an important stage in the sequence of preparatory processes when producing yarns from either one fiber type or a blend of two or more fiber types

It should be evident that important factors in roller drafting are

• The distance between the nip lines (termed the roller setting) in relation

to the distribution of fiber lengths within the sliver

• The applied draft (i.e., the relative roller speeds)

• The number of fibers (or the input count) fed into the drafting zone

Chapter 5 gives an account of drafting theory and considers these factors in more detail

Where the raw material has a broad distribution of fiber lengths, it is sometimes necessary, after the first passage of drawing, to remove from slivers some fibers that are much shorter than the mean length of the distribution The process for doing so

is known as combing, and, as the name implies, a pin surface is used to comb through

the fiber mass of first-passage drawn slivers, removing fibers of preselected short lengths Combing also has the added benefit of contributing to the straightening and alignment of fibers and of removing residual impurities present in the material after the opening, cleaning, and carding stages Combed ring-spun yarns and worsted yarns are produced from combed material, making them of the highest quality in terms of yarn properties, and enabling such yarns to cover the finer end of yarn count range Chapter 5 describes the principles of combing

Following the final passage of drawing, the sliver produced has to be attenuated

to give the required yarn count The most common approach is to attenuate the sliver into a roving and then to attenuate the roving during spinning prior to twist insertion,

or other means, to form the yarn structure Roving production is then the last of the preparatory stages to spinning However, the total required attenuation can be achieved directly from sliver, either with high-draft, roller drafting systems or by pin and saw-tooth-covered rollers, known as opening rollers, used in rotor and friction spinning In Chapter 5, a detailed description is given of the roving produc-

tion process, and Chapter 6 explains the operating principles of opening-roller systems.

The carding process also involves attenuation of the fiber mass to obtain the required sliver count but, as mentioned, few fibers in the card sliver are straight This indicates that drafting during carding is not suitable for fiber straightening From a yarn structure perspective, low fiber straightness and parallelism will sig-nificantly reduce certain important properties (e.g., strength) but increase yarn bulk-iness This yarn characteristic is a requirement for some fabrics and other more technical end uses (e.g., water filtration packs), and a compromise is then reached between yarn strength and bulk The woolen spinning process makes use of the fiber randomness at the card to achieve yarn bulk In this case, the web of carded fibers

is split into thin strands and consolidated to form slubbings, which are subsequently spun into yarns High-bulked yarns are also produced by differential shrinkage of fibers that are obtained by stretch-breaking filaments Chapter 5 describes the stretch-breaking process

Following the ring spinning and any plying processes, yarns are usually rewound

into large-size packages; these usually take the form of a parallel-sided cheese shape

or a cone shape, suitable for use in fabric production and the process of producing such packages is known as winding Winding is important, because it provides the

opportunity for removing imperfections (faults) from the yarn and thereby assists the efficiency of the subsequent processes and improve fabric quality Yarns can also be waxed during winding to improve knitting efficiency The point of importance, however, is that a rewound package is along continuous length of yarn, which enables

a long running time of fabric production The principles of winding are described in Chapter 7 Several spinning systems are, however, able to produce large-size waxed- and unwaxed-yarn packages of the above types, and rewinding then is not practiced

1.7 RAW MATERIALS

The old adage among some yarn spinners, “If it has two ends, it can be spun,” is not strictly true, but it is indicative of the wide range of fiber types and lengths that are today converted into yarns Figure 1.10 charts the broad variety of fiber types that may be converted into yarns It is not the intention to describe the production processes or the detailed chemical properties of these fibers, since the subject of fiber technology would form a textbook in its own right, and indeed many books and scientific papers are readily available for the interested reader; several are cited

at the end of this chapter.8–10 It is, however, appropriate to consider certain aspects

of fiber properties relevant to the production of staple yarns involving those fibers that are used in large tonnages

1.7.1 T HE G LOBAL F IBER M ARKET

The statistics for organic fiber production are regularly reported by Fibre Organon,11ICAC,* and CIRFS†.12–13 The reader may wish, in the future, to keep an updated

* International Cotton Advisory Committee, www.icac.org

check of the production statistics from these sources The latest figures (published

in 2001) at the time of writing this book showed that textile fiber production had reached 57.2 million tons Figure 1.11 illustrates the breakdown of the production tonnage by fiber type, and Table 1.6 lists the main producing countries, Asia and Oceania being the dominant geographical regions

Approximately 90% of world fiber consumption is processed into yarns, 7% into nonwovens, and the remainder used for fillings, cigarette filters, etc Since circa the 1960s, there has been a general growth in world population and an increase in disposable income in the developed economies As a result, consumer demand for easy-care, comfortable fabrics has led to manufactured fibers, largely synthetics, assuming a significantly increased share of world fiber production, accounting for 57% of production, while natural fibers have declined to 43% Of the synthetic fibers,

† Comité International de la Rayonne et des Fibres Synthétiques (International Rayon and Synthetic Fibres Committee), www.cirfs.org

FIBER TYPES

INORGANICS ORGANICS

VEGETABLE

(NATURAL CELLULOSE)

PROTEIN (ANIMAL)

NATURAL POLYMERS

MANMADE POLYMERS

Cellulose Triacetate

(Polyolefins)

Polypropylene

Metals Mohair

Cashmere

Camel

Llama

Alpaca Vicuna

Angora

Polynosic Rayon Lyocell

(High Performance)

e.g., Kevlar, Nomex, PBI, etc.

FIGURE 1.10 Examples of the range of fiber types.

TABLE 1.6

Principal Producing Countries

Country

Synthetics a (× 1000 tons) d

Cotton b (× 1000 tons) Wool

c (× 1000 tons)

a Courtesy of Fibre Organon, June 2000.

b Courtesy of ICAC Washington, August–July 1999/2000.

cCourtesy of Wool Statistics, Greasy Wools 1999/2000, Brussels,

Bel-gium, International Wool Textile Organization.

d 1999 production.

e Excluding polypropylene.

Synthetics [52.4.%] Cellulosics [4.6%] Cotton [33.3%] Wool [2.3%] Jute [5.8%] Linen [1.1%] Ramie [0.3%] Silk [0.1%]

FIGURE 1.11 World production of textile fibers (57 million tons).